3. Measurement setup
No. 99MBA091A
3-3
3.4 Adjusting the Aperture for Transmitted Illumination
The aperture diaphragm for transmitted illumination is used to adjust the Numerical
Aperture (N.A) of transmitted illumination system. It controls the resolution, contrast, and
depth of focus of the optical system.
The diaphragm blades can be seen by removing the eyepiece and looking into the optical
tube with an appropriate light intensity. Adjust the required aperture.
NOTE
Do not set the aperture diaphragm less than 60％ of the radius except for special
types of workpieces. It reduces the resolution. To avoid diffraction, set the
aperture diaphragm more than 15 except for special types of workpieces.
Aperture diaphragm knob for transmitted illumination
Aperture diaphragm blades
Aperture setting for obtaining a
good contrast and image clarity
for ordinary applications:
70 to 80％ of radius
Exit pupil of objective
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